What is the difference between Primary Key and Unique Key?

The primary key and unique key are two essential concepts in a relational database and used to identify a row in a table uniquely. The unique key ensures that no duplicate values are inserted in the database, while the primary and foreign key is responsible for maintaining integrity. The primary key can be a combination of more than one unique key in the same table.

There can only be one primary key per table in the relation database, but there can be more than one unique key per table. The unique key is represented using unique key constraint in any table, and it’s automatically got unique constraint.